Name - Name: Matthew Lingam Course: CE 270 Experiment:...

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Unformatted text preview: Name: Matthew Lingam Course: CE 270 Experiment: Truss Laboratory Exercise Date of Experiment: 1-28-10 Partners: S. Hwang and B. Park Lab Instructor: Matthew Gilbertson Introduction: This lab investigated the amount of force in each member of a truss when a certain force was applied to a joint on the truss. In the experiment, the forces were determined by the strain gauges. These were placed along the members whose forces were then shown on the computer. After the forces of the members were obtained for the two trusses researched, the forces were then calculated by hand. This would give both theoretical forces and experimental forces. The forces were then calculated and a percent of error was found. A prediction is that the experimental accuracy will be fairly accurate, and the percent error will not be more than 10%. Discussion: The reason why the experiment was conducted the way it was, is because it gave a real example of how the forces of different members of the truss would react instead of just having to calculate the forces by hand. Although the calculating was done by hand afterwards to show that the data was fairly accurate. The theoretical analysis ended up being very close to that of the experimental results. The ranges of percent error were between a low of 0.124% and a high of 16.684%. The average percent of error was 3.56% which is fairly low which means the experiment was very accurate. A reason why there would even be a percent of error is because the area of each member is not the same. An average cross sectional area was taken which would have affected the data. Another error that could have affected the data is that the members of the truss do bend, which would affect the forces being calculated by the strain gauges. If the member bends more towards the shape of a “U” than there will be more force at the position were the strain gauges were located which would affect the data. The last of the errors seen could be that the theoretical measurements taken by hand were only rounded out to 3 or 4 decimal places, which could have affected the forces calculated in the long run. As the loads were changed, the axial forces changed in almost the same amount. An example of this is that when the 500lb load was change to 1000lb load the forces would next to double also. It was not terribly exact, but it was a general calculation. When the loads were removed, the forces in all of the members went back down and hovered around 0. The trend was basically a descending one. In the theoretical analysis of the truss, there were a few assumptions that were applied. It was is assumed that there is not bending in the truss, which would end up affecting the results because in reality there is bending in certain members of the truss, which would apply more or less force depending on the way the member bends. The weight of the actual truss is also neglected which would add to the force because of the weight the truss is pulling down on the structure that is holding it up causing the force throughout to be more. Conclusion: This experiment was very successful in the sense that the percent of error was very small. The prediction that was taken at the beginning of the experiment was right for the most part in predicting that the percent error would be less than 10% because the average was 7% less than that of the prediction. There is nothing that has to be altered in this experiment to test the theory more effectively. The results were very accurate, and it would be quite tough to get them any more accurate than they already are. ...
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This note was uploaded on 03/24/2010 for the course ENGR 231 taught by Professor Weiss during the Spring '10 term at Purdue North Central.

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